2031-46-1Relevant academic research and scientific papers
Chiral conflict. The effect of temperature on the helical sense of a polymer controlled by the competition between structurally different enantiomers: From dilute solution to the lyotropic liquid crystal state
Tang, Kai,Green, Mark M.,Cheon, Kap Soo,Selinger, Jonathan V.,Garetz, Bruce A.
, p. 7313 - 7323 (2003)
Helical polymers appended with paired structurally different enantiomers, which have opposing helical sense preferences, yield a new kind of relationship between optical activity and temperature, and also reveal unusual details of the nature of chiral int
Catalytic Regioselective Isomerization of 2,2-Disubstituted Oxetanes to Homoallylic Alcohols
Cabré, Albert,Lledós, Agustí,Rafael, Sergi,Riera, Antoni,Sciortino, Giuseppe,Ujaque, Gregori,Verdaguer, Xavier
, p. 7521 - 7527 (2020/03/24)
The selective isomerization of strained heterocyclic compounds is an important tool in organic synthesis. An unprecedented regioselective isomerization of 2,2-disubstituted oxetanes into homoallylic alcohols is described. The use of tris(pentafluorophenyl
Asymmetric Umpolung Hydrogenation and Deuteration of Alkenes Catalyzed by Nickel
Guo, Siyu,Wang, Xiuhua,Zhou, Jianrong Steve
supporting information, p. 1204 - 1207 (2020/02/04)
Nickel-catalyzed asymmetric hydrogenation of several types of alkenes proceeds in high enantioselectivity, using acetic acid or water as the hydrogen source and indium powder as electron donor. The scope of alkenes herein include α,β-unsaturated esters, n
CuH-Catalyzed Asymmetric Reduction of α,β-Unsaturated Carboxylic Acids to β-Chiral Aldehydes
Zhou, Yujing,Bandar, Jeffrey S.,Liu, Richard Y.,Buchwald, Stephen L.
, p. 606 - 609 (2018/01/26)
The copper hydride (CuH)-catalyzed enantioselective reduction of α,β-unsaturated carboxylic acids to saturated aldehydes is reported. This protocol provides a new method to access a variety of β-chiral aldehydes in good yields, with high levels of enantioselectivity and broad functional group tolerance. A reaction pathway involving a ketene intermediate is proposed based on preliminary mechanistic studies and density functional theory calculations.
Enantioselective β-Protonation of Enals via a Shuttling Strategy
Chen, Jiean,Yuan, Pengfei,Wang, Leming,Huang, Yong
, p. 7045 - 7051 (2017/06/01)
Remote asymmetric protonation is a longstanding challenge due to the small size of protons. Reactions involving electron-deficient olefins pose a further difficulty due to the electrophilic nature of these substrates. We report a shuttling system that delivers a proton in a highly enantioselective manner to the β-carbon of enals using a chiral N-heterocyclic carbene (NHC) catalyst. Choices of a Br?nsted base shuttle and a Br?nsted acid cocatalyst are critical for highly stereoselective β-protonation of the homoenolate intermediate and regeneration of the NHC catalyst results in functionalization of the carbonyl group. Thioesters with a β-chiral center were prepared in a redox-neutral transformation with an excellent yield and ee.
Enantioselective Hydrogenation of β,β-Disubstituted Unsaturated Carboxylic Acids under Base-Free Conditions
Yan, Qiaozhi,Kong, Duanyang,Zhao, Wei,Zi, Guofu,Hou, Guohua
, p. 2070 - 2077 (2016/03/15)
An additive-free enantioselective hydrogenation of β,β-disubstituted unsaturated carboxylic acids catalyzed by the Rh-(R,R)-f-spiroPhos complex has been developed. Under mild conditions, a wide scope of β,β-disubstituted unsaturated carboxylic acids were hydrogenated to the corresponding chiral carboxylic acids with excellent enantioselectivities (up to 99.3% ee). This methodology was also successfully applied to the synthesis of the pharmaceutical molecule indatraline.
Asymmetric hydrogenation of allylic alcohols using ir?N,P-Complexes
Li, Jia-Qi,Liu, Jianguo,Krajangsri, Suppachai,Chumnanvej, Napasawan,Singh, Thishana,Andersson, Pher G.
, p. 8342 - 8349 (2018/05/23)
In this study, a series of γ,γ-disubstituted and β,γ-disubstituted allylic alcohols were prepared and successfully hydrogenated using suitable N,P-based Ir complexes. High yields and excellent enantioselectivities were obtained for most of the substrates studied. This investigation also revealed the effect of the acidity of the N,P?Ir-complexes on the acid-sensitive allylic alcohols. DFT ΔpKa calculations were used to explain the effect of the N,P-ligand on the acidity of the corresponding Ir-complex. The selectivity model of the reaction was used to accurately predict the absolute configuration of the hydrogenated alcohols.
CROSS-COUPLING OF UNACTIVATED SECONDARY BORONIC ACIDS
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Page/Page column 56; 57, (2015/05/19)
Provided are methods for site- and stereo-retentive cross-couplings with unactivated secondary boronic acids, particularly useful in building block-based approach for small molecule synthesis. Also provided is a method of forming an air-stable chiral secondary boronic acid.
Iridium catalysts with Chiral bicyclic pyridine-phosphane ligands for the asymmetric hydrogenation of olefins
Quan, Xu,Parihar, Vijay Singh,Bera, Milan,Andersson, Pher G.
, p. 140 - 146 (2014/01/06)
New bicyclic pyridine-phosphane ligands were prepared, and their iridium complexes were evaluated in asymmetric hydrogenation of trisubstituted olefins with non-coordinating and weakly coordinating substituents. The iridium catalysts showed high reactivity and enantioselectivity for both types of olefins. New pyridine-derived N,P-chelated iridium catalysts were prepared and evaluated in the asymmetric hydrogenation of trisubstituted olefins. High conversions and enantioselectivities were obtained. Copyright
Iridium-catalyzed asymmetric hydrogenation of 3,3-disubstituted allylic alcohols in ethereal solvents
Bernasconi, Maurizio,Ramella, Vincenzo,Tosatti, Paolo,Pfaltz, Andreas
supporting information, p. 2440 - 2444 (2014/03/21)
Ir-phosphinomethyl-oxazoline complexes have been identified as efficient, highly enantioselective catalysts for the asymmetric hydrogenation of 3,3-disubstituted allylic alcohols and related homoallylic alcohols. In contrast to other N,P ligand complexes, which require weakly coordinating solvents, such as dichloromethane, these catalysts perform well in more ecofriendly THF or 2-MeTHF. Their synthetic potential was demonstrated with the formal total synthesis of four bisabolane sesquiterpenes. Particularly high enantioselectivity values in the asymmetric hydrogenation of 3,3-disubstituted allylic alcohols and related homoallylic alcohols have been achieved with Ir-phosphinomethyloxazoline catalysts. In contrast to other N,P-ligand complexes, which require weakly coordinating solvents, such as CH 2Cl2, these catalysts perform well in more ecofriendly THF or 2-MeTHF (see scheme; CODa =a 1,5-cyclooctadiene). Copyright
